border-1px($color)
	position 
	&:after
		display: block
		position: absolute
		left: 0
		bottom: 0
		widows:100%
		border-top:1px solid $color
		content: " "

border-none()
	&:after
		display none

bg-image($url)
	background-image:url($url+'@2x.png')
	@media (-webkit-min-device-pixel-ratio:3),(min-device-pixel-ratio:3)
		background-image:url($url+'@3x.png')